Self-propelled combines have headers equipped with skid plates located below and rearwardly of the crop cutting knives and guards. The skid plates are metal members which collect soil that can interfere with the crop cutting operation of the header and power required to propel the combine. The skid plates must be cleaned to overcome the adverse operation of the combine. The combine is shut down to allow the operator to remove soil and debris from the skid plates. Plastic covers or panels have been used with the skid plates to prevent adhesion of soil to the plates and panels. T. D. Rabitsch in U.S. Pat. No. 4,729,212 discloses covers for combine skid plates made from ultra high molecular weight polyethylene plastic which has a low coefficient of friction. Soil, such as wet clay, does not adhere to the plastic covers. Each cover has an upper surface that mates with the outer surface of a conventional skid plate and an outer surface substantially parallel to the upper surface. The cover has uniform thickness as it is cold pressed from a sheet of plastic. This cover does not compensate for uneven wear of the cover due to soil and stone abrasion. T. D. Rabitsch in U.S. Pat. No. 5,174,101 discloses plastic covers for combine skid plates that have uniform thickness and transverse live hinges to compensate for varying tolerances of the skid plates to achieve mating engagement between the covers and skid plates. The live hinges have transverse grooves in the outer surfaces of the cover which can collect soil and debris. These plastic covers are stamped or cold pressed from a sheet of plastic having uniform thickness. The stamped covers cannot have increasing thickness along their length to compensate for wear. The plastic has memory characteristics which cause the plastic to return to its original flat shape. The covers have inconsistent shapes which do not allow for mating engagement with the combine skid plates. The skid shoes of the invention are improvements in plastic skid shoes that obviate the problems of the prior covers for combine skid plates.